Surface and sub-surface oceanic conditions across the Tropical Pacific
remained slightly warmer than average during December 2003 (Table
T2),
while atmospheric features continued to reflect ENSO-neutral conditions (Table
T1). Although sea surface temperature (SST) anomalies remained above
average across the entire equatorial Pacific, the departures across the
central Pacific decreased from November (Fig. T5). The largest SST
departures (exceeding 1°C) remained
in the western Pacific between 160°E
and the date line (Fig. T18).

Oceanic thermocline depths, measured by the depth of the 20°C
isotherm (Figs. T15, T16), remained slightly deeper than average
across most of the equatorial Pacific during December. Thermocline depths
have been slightly deeper than normal across most of the equatorial Pacific
since May (Fig. T15). Consistent with these conditions, oceanic
temperatures at thermocline depth remained 1-2̊C
above average across most of the equatorial Pacific (Fig. T17).

The low-level (850-hPa) equatorial winds were stronger than average
across the central and western Pacific and near average over the eastern
Pacific during December 2003 (Fig. T20, Table T1). The index values
in the western and central Pacific regions are the largest since April and
February 2001, respectively (Fig. T4). The Tahiti-Darwin SOI was 1.1
during the month, the largest value of this index since February 2001. These
indices have, however, exhibited large week-to-week variability since late
November, in response to stronger intraseasonal (Madden-Julian Oscillation)
activity (Figs. T12, T13).

Tropical outgoing longwave radiation (OLR) anomalies were negative
(enhanced cloudiness and precipitation) over Indonesia, northern Australia,
and near 10°N across the central
Pacific and positive along and just south of the equator near the date line
(Fig. T25). Tropical convection was also influenced by intraseasonal
activity during the month, although there continues to be a tendency for
enhanced equatorial convection to persist over the Pacific between 130°E
and 160°E (Fig. T11).